As benzene derivatives, known are compound A (see J. Nat. Prod., 1985, Vol. 48, pp. 660-663), compound B, (see U.S. Pat. Nos. 3,118,887, 3,268,474, and the like), compound C (see Tetrahedron Lett., 1999, Vol. 40, pp. 4769-4773), etc.

Benzoquinone ansamycin antibiotics such as Geldanamycin, Herbimycin, etc. and Radicicol are known as compounds which are bound to heat shock protein 90 (Hsp90) family proteins (Cell Stress & Chaperones, 1998, Vol., 3, pp. 100-108; J. Med. Chem., 1999, Vol., 42, pp. 260-266); and purine derivatives and pyrazole derivatives are also known (WO03/037860, WO03/055860). It is reported that these compounds are all bound to Hsp90 family proteins and inhibit the functions of Hsp90 family proteins, thereby exhibiting pharmacological activities such as anti-tumor activity. Therefore, compounds capable of being bound to Hsp90 family proteins are considered to be useful as therapeutic agents for diseases associated with Hsp90 family proteins or proteins to which Hsp90 family proteins are bound (Hsp90 client proteins).
Examples of known Hsp90 family proteins include Hsp90α protein, Hsp90β protein, grp94 and hsp75/TRAP1 (Pharmacology & Therapeutics, 1998, Vol., 79, pp. 129-168; Molecular Endocrinology, 1999, Vol., 13, pp. 1435-1448; etc.).